Fluid flow electric switch and method of and apparatus for manufacture of same



, 1937. w R. WALKER 2,101,114

FLUID FLOW ELECTRIC SWITCH AND METHOD OF AND APPARATUS FOR MANUFACTUREOF SAME Filed June 26, 1935 2 Sheets-Sheet 1 .INVENTOR 28/ G2. IX/MmTORNEY Dec. 7, 1937. w. R. WALKER FLUID FLOW ELECTRIC SWITCH AND METHODOF AND APPARATUS FOR MANUFACTURE OF SAME Filed June 26, 1935 2Sheets-Sheet 2 I? %f a? 5 INVENTOR Patented Dec. 7, 1.937

UNITE-o STATES PATENT err-" ce FLUID FLow ELECTRIC swr'ron Ann mz'rnopOFAND APPARATUS son. MAN- UFACTURE OF SAME Warren R. Walker-,ShortHills, N. J., assignor to" General Electric Vapor Lamp Company, Ho-'boken, N. J., a corporation of New Jersey Application June 2c, 1935,Serial No. 28,560

12 Claims.

vide a fluid flow switch havingan extremely low internal resistance.Another object of my 'in-.

vention is to provide a compact fluid flow switch which willv have along useful life. Another object of my invention is to provide a fluidflow switch requiring only a small angular movement to secure operationthereof. A further object of my invention is to provide a novel methodand apparatus for the manufacture of a fluid flow switch. Still otherobjects and advantages of my invention will appear from the followingdetailed specification or from an inspection of the accompanyingdrawings.

The invention consistsin the new and novel structure and apparatus, andin the novel steps of the method, as hereinafter set forth and claimed.

It has long been the goal of those interested in the development ofmercury switches to produce a switch which not only would combine thestrength of a substantially all-metal envelope with the many well knownadvantages of the hermetically sealed vitreous envelope type nowon themarket, but which would also be adaptable to mass production byautomatic machinery. Many efiorts have been made heretofore to developsuch a switch,but none of theseprior efforts has resulted in commercialsuccess, 'due to the many difliculties involved.

One of these difliculties is the high internal resistance resulting fromthe oxidation of the metal inleads during the fabrication of the switch.

Where the vitreous portion of the envelope vastly exceeds the metal; asin the switches now on the market, this oxide is easily eliminatedbycleaning the inleads after'they have been sealed into the envelope andthen finally closing the envelope at a point remote from the metalinleads,.but as the relative proportion of the metal to glass in- 1creases this elimination of oxide becomes increasingly diflicult. Thuswhen the vitreous portion of the envelope has been reduced to theminimum consistent with proper insulation of the 1 parts and the inleadshave been expanded in area until they form virtually the entireenvelope, as in the preferred case, it'is obviously impossible to usethis cleaning method of the prior art. The oxide which thus remained inthe finished switch has greatly increased the internalresistancethereof', and has necessitated special and. expensivetreatment of the switch to even partially renovel materials.

necessary to use the more refractory glasses for duce' this resistanceto the value that would be obtainable with unoxidized'electrodes.

I 'have nowdiscovered thatthis difficulty is overcome by constructing myfluid flow switch of Thus heretofore it has been the envelopes ofmercury switches and the like.

I have now found, however, that with the novel switch structure which Iemploy extremely satis factory results are produced with a glass havinga low melting point, far below that of any glass heretofore used formercury switches, due to the fact that this'glass is here almostcompletely shielded from, the arc. With this low meltin point glass theswitch is fused together ,at' a temperature below that at which anyappreciable oxidation of the electrodes is produced. Other thermoplasticmaterials of low fusing point may likewise be used with this novelconstruction with similar results. As a further precaution I prefer toplace the portion of the metal housing which is destined to make contactwith the mercury in good thermal contact with a body of large thermalcapacity, during the fusion process,

whereby these parts are maintained at an even lower temperature thanthat at which the fusion of the parts occurs.

virtually free of oxide and hence have an extremely low resistance.

the glass seal is made relatively long, ascompared to the actualseparation of the metal portions, and at the same time the amount ofsaid seal which is exposed either on the interior or As a result of thisnovel structure, and procedure my novel switches are f In thenovel'structure which I preferably use the exterior of the switch iskept very small. -I- have found that with this novel construction theswitch remains effectively sealed, even after long periods of hardusage, despite the low melting point of the glass employed. A convenientway ofv producing this result is to form the refractory dividingmemberwhich is commonly used with a rounded edge of substantially thesame diameter as the thickness of said membenthe metal parts also beingformed with a flange of the same curvature. the refractory member alongthis entire curved The metal parts are then sealed to surface by meansof the low melting point glass,

the result being a very'thin seal of a length at any point which is ofthe order of three fourths the thickness of the refractory member. Thislong seal is. obtained with this novel construction without anobjectionable increase in the dimensions of the 1 switch. Furthermore,due to the shape of the seal this novel structure is unusually'strongandresistant to shocks, since it is well adapted to resist stresses inanydirection. t I have found that the thin coating of-glass' which is thusemployed between the-refractory member and the metal parts is veryconveniently produced in a novel manner by rotating said member with theedge thereof immersed in a molten bath of the desired glass. Thisproduces a very thin coating, with some of the glass penetrating thepores of the refractory member, which has been found to giveexceptionally good results. In some cases, however, this refractorymember is entirely covered with a glaze which can be used to fuse themetal members thereto, this glaze being produced in any suitable manner.

In any of these switches where the size is reduced as much as possiblein the interest of compactness there is an objectionable tendency toincrease the angle of rotation necessary to produce operation of theswitch. I have found that this difficulty is overcome by placing theopening in the refractory member as close to the outside edge of themercury retaining chamber as is consistent with the necessary strengthof the member, and by further providing this opening with a novel shape.Thus the outside edge of this opening is preferably made tosubstantially follow an are drawn about the axis of the refractorymember, while the remainder of the opening extends in any desired shapeto a point above the level attained by the mercury when it is all on oneside of the member, whereby gas can always readily flow therethrough topermit equalization of the mercury level on opposite sides of saidmember. I have furthermore found that the refractory member is moreresistant to strain if the corners of this opening are rounded slightly,and that this desirable result can be attained without in any wayaffecting the sensitivity of the switch by making the radius ofcurvature at the ends of the arcuate section conform to theshapenaturally assumed by the mercury because of the high surface tensionthereof. In general I prefer to make the sides of this openingsymmetrical since this greatly facilitates the manufacturing procedure,the preferred opening being roughly triangular.

For the purpose of illustrating my invention I have shown a preferredembodiment, together with the novel apparatus used in the manufacturethereof, in the accompanying drawings, in which Fig. 1 is a sectionalview of my novel switch,

tional views of the apparatus used to assemble the switch, and

Fig. 8 is a sectional view of one of the work holding chucks showing themanner in which the switch parts are supported therein.

As particularly shown in Figs. 1 to 4 my novel switch is formed of twodished metal members I and 2, which are identical save that the member Ihas an opening therein, a refractory dividing member 3, mercury 6, ametal ball 5 welded into the opening in the member I, and a thin coating6 of glass or other thermoplastic material between the refractory 3 andthe metal members I and 2. These metal members are each preferably drawnfrom sheet metal and have a short cylindrical section, say inch long andinch in diameter, one end of which is closed with a flat wall having areentrant boss therein whichis adapted to cooperate with the mountingmeans, while the other end is flared outwardly in an arc ofapproximately 90 with a radius of approximately of an inch, as shown inFigs. 1 and 4. i The refractory member 3 is made in the form of fractorymember 3, said opening extending close to the rounded portion thereof.

Said opening is roughly triangular in shape, although the corners areslightly rounded, with a radius of say inch, and the edge thereof whichis adjacent the rim of the refractory member 3 follows an arc ofapproximately 50 which is concentric with the refractory member 3. Sincethe chord deviates but little from the arc with this angle and radius, Ifind that the chord may be followed by this opening with substantiallythe same resuits, and I include this variation in the claims when Irefer to the rim of this opening as being substantially arcuate. Asshown the apexof this opening does not quite reach the center of themember 3, although the exact position thereof is not extremelyimportant, so long as it is far enough from the edge to permit free flowof the mercury under all conditions.

The glass 8 which is used to fuse the foregoing parts togetherpreferably consists of a glass having an extremely low softeningtemperature, so that the metal members I and 2'will not be oxidizedduring the fusion process. It likewise must have a suitable coefficientof expansion and must wet the metal members I and 2 so as to form a goodseal. Thus when the metal members I and 2 are made of an alloy producedby the Allegheny Steel Company and known as Allegheny 55, this being a26% chrome-iron alloy with a typical analysis as follows:-

Carbon -Junder- .25 Manganese do 1.00 Sulphur do .025 Phosphorus do .025Silicon do .60 Chromium 26.00-30.00 Nickel -under- .60

it has been found that a glass having the following composition givesexceedingly good results:

Percent SiOz 27 N320 8 02.0 2 MgO 1 A1203 -Q 1 PbO 44 B203 17 This glasshas a softening temperature of less than 450 C., so that the switch canbe fused together therewith without heating the metal even to a redheat, the oxidation thereof during the fusion process thus beingvirtually eliminated. Furthermore the coefiicient of expansion of thisglass almost exactly matches that of the metal, so that no strains areproduced in the switch which might result in breakage thereof. Withthis'combination of metal and glass I prefer to make the refractorymember 3 of the following composition:

Percent MgO '15 Ball clay j Feldspar 10 After this has been fired at1155 C. for 120 hours this refractory has a coefflcient of expansionwhich closely matches that of the glass and the metal. I a

In place of this low melting point glass other thermoplastic materials,such as vinyl acetate and related compounds may also be used withspindle III of the apparatus shown in Fig. 5.

This spindle is driven by a motor II through suitable reduction gearingand the belt I2. Said sp ndle has an axial opening therethrough which isconnected through the cooling coil I3 and the tube I4 to a. vacuumsystem, whereby said spindle serves as a vacuum chuck, a lug beingprovided on the end thereof which engages the opening 8 in therefractorymember 3 to accurately position sa d member on said spindle. Air isconveniently supplied through the nozzle I5 to cool the coil I3, andfins I6 are likewise provided on the spindle III to keep the supportbearings cool. A crucible ll of molten glass is mounted within theelectric furnace III which is supported on a cam Is. Said cam isconnected to a handwheel 20, and is adapted upon rotation to raise thecrucible I'I until a refractory member 3 on the spindle I0 will rotatewith its rounded edge immersed therein. A support 2I rotatably carries aset of gas, jets 22 which are adapted to impinge upon a refractorymember 3 carried by the spindle Ill, and upon the surface of the glassin the crucible I! when the latter is in its'elevated position. wherebythe re fractory is kept at such a temperature that the glass flowsevenly over the edge thereof, as shown in Fig.3.

After the refractory member 3 has been placed upon the spindle III thelatter is rotated and the jets 22 are adjusted to impinge thereon. Assoon as said member is sufficiently hot the handwheel is operated toraise the crucible II until the entire rounded edge of said member hasbeen immersed therein to produce the coating 6, after which the crucibleis again lowered. In practice the member 3 is allowed to continuerotating for a short intervalin the flames from the jets 22, while theglass coating sinks somewhat into the pores ofthe refractory member 3,since this has been found to give better results.

While the refractory isthus being coated the metal members I and 2 areplaced in the chucks 25 and 26 of the apparatus shown in Figs. 6 and '7.Said chucks are similar except that the upper chuck 26. has an opening2-1 therethroughwhich is connected in a. suitable manner with a vacuumsystem, whereby the member 2 is retained were ',in by suction. Asparticularly shown in Fig. 8

these chucks are relatively massive and make a snug fit with thecylindrical portion of the metal therebetween. The'chuck 25 is mountedon a horizontal arm28 which is in turn carried. by the vertical slidemember 29. The latter member operates in suitable channels in thevertical support 30,and has a rack 3| thereon which cooperates with apinion 32 operated by the handwheel 33. The chuck 26 is carried by a.similar horizontal arm 34 which is in turn attached to the member 35which slides in suitable channels in the slide member 29, sufiicientfriction being provided therebetween to cause said members 29 and 35 tomove together in response to the operation of the hand-wheel 33. Ahandgrip 36 is provided on the member 35 to provide a method of movingthe chuck 25 with respect to the chuck 26, while a parallel handgrip 31on the slide member 29 provides a convenient means to exert considerablepressure between the aforesaid chucks when said handgrips are bothgrasped by the same hand and squeezed together. A vertical support 38carries at its upper end a horizontal arm 39 which slidably supports themember 40, the latter in turn carrying theburner 4| having a series ofjets converging from all sides toward a common point.

Theparts I and 2 are loaded into the chucks 25 and 26 while this burner4| is in the position shown in Fig. 6, after which this burner is slidto the position shown in Fig. '7. The hand-wheel 33 is then moved tobring'the metal shell I into range of the flames from the burner 4|, anda coated refractory member 3 with the glass coating 6 still soft isalmost immediately laid thereon, a vacuum wand having a pick-up portionsimilar to the end of the spindle Ill preferably'being used for thispurpose. The handgrip 36 is then moved to bring the metal shell 2 downinto contact with the coating Ii on this refractory member. After ashort heating period the handgrips 36 and 31 are squeezed together toput pressure on the metal shell 2, forcing the parts of the switch intothe intimate contact shown in Fig. 1. The handwheel 33 is then operatedto lower the switch assembly until the burner 4| can pass above thechuck 26, after which said burner is retracted to the position shown inFig. 6, and the switch removed; In some cases this assembly is thenannealed in a suitable furnace in order to eliminate the possibility ofstrains.

The assembled switch is then evacuated in any suitable manner throughthe opening in the metal shell, and the desired quantity of mercuryinsorted therethrough, together with an arc suppressing atmosphere suchas hydrogen or anhydrous ammonia at a pressure of the order of one ortwo atmospheres, although when desired the device can be left evacuatedand successfully used bled with the indents opposite each other and at agiven angle of rotation with respect to the opening 8 in the refractorymember 3. Ihis assembly is greatly facilitated by providing the chucks25 and with internal bosses which engage these indentsand thus ensure afixed position of the metal shells therein.

Due to the unusually low. temperature required to fuse the glass 6, andto the presence of the chucks of high thermal capacity, which serve torestrict the temperature rise, the cylindrical and end portions of themetal shells l and 2 are. not appreciably Oxidized during the fusion ofthe elements, so that the internal resistance thereof is extremely low.The use of this low melting point glass does not in any way reduce theuseful life of these switches, however, due to the fact that with mynovel structure only an extremely small portion of the long vitreousseal is exposed to the arcs therein. The working temperature of theseswitches furthermore seldom, if ever reaches 100 C., so that there is nodanger of the glass softening during operation. As a further advantageof this structure only a small amount of this glass is exposed on theexterior of the switch, although the seal itself is relatively long, ascompared to the amount thus exposed.

The angular movement necessary to operate my novel switchis relativelysmall, of the order of only 30, in spite of its compact size, due to theshape and location of the opening 8 in the refractory member 3. As aresult of these two features, which have heretofore never been attained.together, my novel switch is especially adapted for use in wallswitches and other similar places where mercury switches have not beenextensively used heretofore because of their bulkiness.

While I have described my invention by reference to a specificembodiment thereof it is to be understood that various changes,substitutions and omissions, within the scope of the appended claims,may be made in the structure and in the steps of the method withoutdeparting from the spirit of my invention. I

I claim as my invention:

1. An electric switch comprising the combination of an apertured disc, apair of metallic members whose rims are shaped to closely fit the edgesof said disc for an' appreciable distance without making contact witheach other, a thin coating of thermoplastic insulating material betweenthe overlapping portions of said disc and each of said metallic members,whereby the fore going elements comprise a hermetically sealed envelopehaving two chambers connected by the aperture in said disc, saidthermoplastic material having a composition which is workable tohermetically seal said envelope at a low temperature, and mercury withinsaid envelope to connect said metallic members through said aperture inone position of said switch.

2. An electric switch comprising the combination of an apertured disc ofrefractory material, the edges of said disc being rounded, a pair ofdished metallic members whose rims are shaped to fit the rounded edgesof said disc without making contact with each other, a coating ofthermoplastic insulating material between the overlapping portions ofsaid disc and each of said metallic members, said coating covering theentire rounded surface of said disc whereby the foregoing elementscomprise a hermetically sealed envelope having two chambers connected bythe aperture in said disc, and mercury within said envelope to connectsaid metallic members through said aperture in one position of saidswitch.

3. An electric switch of the fluid flow type comprising the combinationof an apertured ceramic disc, a pair of dished metal members on oppositesides of said disc and fused thereto by a thin layer of glass, thecoefficients of expansion ofsaid disc, said metal members and said glassbeing similar, said glass being of a composition which is workable tohermetically seal said switch at a temperature at which said metalmembers are not appreciably oxidized in air, and a quan tity of mercurysufficient to close a circuit through the aperture in said disc betweensaid metal members.

4. The method of producing the casing of anelectric switch of the fluidflow type which comprises dipping the periphery of an apertured ceramicdisc into a bath of molten thermoplastic material to produce a coatingof said material thereon, and fusing a metal member to said materialonopposite sides of said disc to form an envelope having two chambersconnected by the aperture in said disc.

5. The method of producing the casing for an electric switch of thefluid flow type which comprises coating the periphery of an aperturedceramic disc with molten glass, and fusing a dished metal member to saidglass on opposite sides of said disc while said glass is still molten toform an envelope having two chambers connected by the aperture in saiddisc.-

6. The method of producing the casing for an electric switch of thefluid flow type which comprises coating the periphery of an aperturedceramic disc with molten glass, fusing a dished metal member to saidglass on opposite sides of said disc to form an envelopehaving twochambers connected by the aperture in said disc, and restricting thetemperature rise of a portion of said metal members during the aforesaidfusion process to prevent oxidation of the interior surface thereof.

7. The method of producing a casing for an electric switch of the fluidflow type which com prises fusing two dished metal members to a ceramicdisc with a thermoplastic material, and restricting the temperature riseof a portion of each of said metal members during said fusion process toprevent oxidation of the interior surface thereof.

8. In apparatus for producing an electric switch of the liquid flowtype, in combination, means to support a pair of dished metallic membersin such a position that a glass coated ceramic disc can be laid upon oneof said members, means to move the other of said members into contactwith the coating on said disc, and means to heat the coating on saiddisc and the portion of said metal members in contact therewith toperfect the fusion of said parts to form a switch envelope, saidsupporting means having an appreciable thermal capacity and beingrecessed to permit the snug insertion therein of substantially all ofsaid metal members except that portion thereof which is being fused tosaid glass, whereby oxidation of the interior of said switch envelopeduring the fusion process is substantially prevented.

9. In apparatus for producing an electric switch of the liquid flowtype, in combination,

' means to dip an apertured ceramic disc into a path of molten glass tocoat the edge thereof with said glass, means to support a pair of dishedmetallic members in such a position that said coated disc can be laidupon one of said members, means to transfer said coated disc to saidmember while the coating thereon is still molten, means to move theother of said members into contact with the coating on said disc, andmeans to heat said coating and the metal in contact therewith to perfectthe fusion of said parts to form a switch envelope.

:10. An electric switch comprising the combination of an aperturedrefractory body, a pair of metallic members whose rims are shaped toclosely fit said body for an appreciable distance away from the edge ofsaid members without making contact with each other, a thin coating ofthermoplastic material between the overlapping portions of said body andeach of said metallic members, whereby the foregoing elements comprise ahermetically sealed envelope having two chambers connected by theaperture in said body, said thermoplastic material having a compositionwhich is workable to hermetically seal said envelope at a lowtemperature, and mercury within said envelope to connect saidmetallicmembers through said aperture in one position of said switch. v

11. An electric switch comprising the combination of an aperturedrefractory bodina pair of metallic members whose rims. are shaped toclosely fit said body for an appreciable distance away from the edge ofsaid members without making contact with each other, a thin coating ofthermoplastic material between the overlapping portions of said body andeach of said metallic members, whereby the foregoing elements comprise ahermetically sealed envelope having two chambers connected by theaperture in said body, and

mercury within said envelope to connect said metallic members throughsaid aperture in one position of said switch, said body having abutmentson either .side thereof against which the edges of said metallic membersrest to determine both the separation of said metallic members and thethickness of the thermoplastic coating between each of said members andsaid body.

12., An electric switch comprising the combination of an apertured bodywhose thickness adjacent the rim thereof decreases progressively in thedirection of the rim, 9, pair of metallic members whose rims are shapedto closely fit the edges of said body for an appreciable distance awayfrom the rim thereof, a thin coating of thermo-' plastic -materialbetween each of said metallic members and said body throughout the areawhere they closely fit each other, whereby the foregoing elementscomprise a hermetically sealed envelope having two chambers connected bythe aperture in said body, and mercury within said envelope to connectsaid metallic members through said aperture in one position of saidswitch, said refractory body having abutments on either side thereofagainst which the edges of said metallic members rest to determine boththe separation of said metallic members and the thickness of thethermoplastic coating between each of said metallic members and saidbody.

WARREN R. WALKER.

